Strategic combination of Grignard reagents and allyl-functionalized ionic liquids as an advanced electrolyte for rechargeable magnesium batteries

Ionic liquids are effective additives in terms of improving the key electrolyte properties including the ionic conductivity and the oxidative solubility of Grignard reagent-based electrolytes for rechargeable magnesium batteries. However, a precise understanding of their working mechanisms remains elusive to date. Here, we unravel for the first time the mechanism behind the drastic improvement of key electrolyte properties of Grignard reagents upon the addition of allyl-functionalized pyrrolidinium-based ionic liquids. We show that the Grignard reagents selectively abstract acidic protons in the allyl functional group to create a series of Mg-complexes that are remarkably stabilized by the formation of resonance structures. Moreover, the properties of the resulting electrolytes are tuned by adjusting the molar concentration of the ionic liquids which determines the chemical reaction pathway for the formation of new Mg-complexes. Overall, this study demonstrates a novel strategic approach for developing highly efficient new electrolyte systems for rechargeable magnesium batteries.